1. Field of the Invention
This application relates to the art of optical waveguides that may include a flat optical waveguide connected with channel optical waveguides, and that may reduce optical leakage from a clearance gap of a bonding face between a channel optical waveguide and a flat optical waveguide.
2. Description of the Related Art
Related art that uses Silicon (Si) as a waveguide material is useful for downsizing and mass production of optical circuits. In a Si photonic wire line optical waveguide, the entire circumference of the core of the Si is covered with a cladding of silicon dioxide (SiO2). The difference in the index of refraction respectively of the core (e.g., Si) and cladding (e.g., SiO2) is large enough that the Si photonic wire optical waveguide may guide optical signals with relatively small size. The Si photonic wire optical waveguide may also curve so as to bend an optical signal in a small radius of curvature of approximately 1 μm. This small radius of curvature is made possible by the core-cladding refractive index difference. The Si photonic wire optical waveguide may also have a submicron cross section structure that is small, because the Si photonic wire optical guide may be manufactured using processing techniques associated with Silicon electronic device.
Japanese Laid-Open Patent No. 2001-159718, and the publication, Journal of Selected Areas in Quantum Electronics, vol. 16, p. 33, 2010, describe a wavelength separation element as an application example of the Si fine line optical waveguide. The wavelength separation element described in this literature is called a “Arrayed Waveguide Grating (AWG)”. The AWG may be configured by a flat optical waveguide connected to channel optical waveguides. In the AWG that uses the Si photonic wire optical waveguide, there is a problem that many optical leaks occur at clearance gaps formed between edges of the channel optical waveguides adjacent the flat optical waveguide and the flat optical waveguide.
In the publications discussed above, the channel optical waveguide has a taper shape in the thickness direction thereof to prevent optical leakage. However, the AWG described by the publications must form a base plate in the thickness direction thereof, so that both the structure and manufacturing process of the channel optical waveguide are complex.